È. M. Belenov, S. V. Grigor'ev, A. V. Nazarkin, I. V. Smetanin, “Optically pumped x-ray free-electron laser as a two-level quantum oscillator with a completely inverted active medium”, Kvantovaya Elektronika, 17:7 (1990), 815–816 [Sov J Quantum Electron, 20:7 (1990), 733–734]
Contact us: